The present invention is directed to a method and device that frequency modulates an input signal that operates a high intensity discharge (HID) lamp to thereby generate a frequency modulated output signal that drives an arc of the lamp.
An arc of a HID lamp may be driven with a high frequency signal; that is, a signal whose current is generally sinusoidal or triangular and has a frequency in the range of about 100 kHz to 300 kHz with no, or nearly no, DC component in the current. A high frequency signal for driving an HID lamp is desirable because such signals may be generated with components that are generally smaller and cheaper than those that generate lower frequency signals. However, high frequency signals are accompanied by acoustic resonance phenomena that appear strongly in HID lamps.
Frequency modulation of the signal that drives the arc of the lamp is a known technique for at least partially avoiding acoustic resonance when an HID lamp is driven with a high frequency signal. Modulation methods and devices tend to be complicated and costly, especially when attempting to develop a device that is useful in various HID lamps. Acoustic resonance frequencies vary from lamp to lamp and within a lamp depending on lamp temperature.